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<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>6-4 立方体绘制（顶点法）</title>
  <script src="../lib/index.js"></script>
  <style>
    * {
      margin: 0;
      padding: 0 !important;
    }
    body {
      border: 1px solid #ccc;
    }
    #canvas {
      margin: 50px auto 0;
      display: block;
      background: yellow;
    }
  </style>
</head>
<body>
  <canvas id="canvas" width="400" height="400">
    此浏览器不支持canvas
  </canvas>

  <script>
    const ctx = document.getElementById('canvas');
    const gl = ctx.getContext('webgl');

    /**
     * 创建着色器源码
     * */
    // 顶点着色器
    // gl_Position vec4(0.0, 0.0, 0.0, 1.0) x, y, z, w齐次坐标（x/w, y/w, z/w）
    const VERTEX_SHADER_SOURCE = `
      attribute vec4 aPosition;
      attribute vec4 aColor;
      varying vec4 vColor;

      uniform mat4 mat;
      void main() {
        gl_Position = mat * aPosition;
        vColor = aColor;
      }
    `;

    // 片元着色器
    // gl_FragColor vec4(1.0, 0.0, 0.0, 1.0) r, b, g, a
    const FRAGMENT_SHADER_SOURCE = `
      precision lowp float;
      varying vec4 vColor;

      void main() {
        gl_FragColor = vColor;
      }
    `;

    /**
     * 创建着色器
     * */
    const program = initShader(gl, VERTEX_SHADER_SOURCE, FRAGMENT_SHADER_SOURCE);

    const aPosition = gl.getAttribLocation(program, 'aPosition');
    const aColor = gl.getAttribLocation(program, 'aColor');
    const mat = gl.getUniformLocation(program, 'mat');

    // 创建三角形系列数据

    // 顶点
    const v0 = [1,1,1];
    const v1 = [-1,1,1];
    const v2 = [-1,-1,1];
    const v3 = [1,-1,1];
    const v4 = [1,-1,-1];
    const v5 = [1,1,-1];
    const v6 = [-1,1,-1];
    const v7 = [-1,-1,-1];
    const points = new Float32Array([
      ...v0,...v1,...v2, ...v0,...v2, ...v3, // 前
      ...v0,...v3,...v4, ...v0,...v4, ...v5, // 右
      ...v0,...v5,...v6, ...v0,...v6, ...v1, // 上
      ...v1,...v6,...v7, ...v1,...v7, ...v2, // 左
      ...v7,...v4,...v3, ...v7,...v3, ...v2, // 底
      ...v4,...v7,...v6, ...v4,...v6, ...v5, // 后
    ]);

    // 创建缓冲区对象
    const buffer = gl.createBuffer();

    const BYTES = points.BYTES_PER_ELEMENT;

    // webgl关联缓冲区对象
    gl.bindBuffer(gl.ARRAY_BUFFER, buffer);

    // 顶点数据写入缓冲区对象
    gl.bufferData(gl.ARRAY_BUFFER, points, gl.STATIC_DRAW);

    // 给attribute变量赋值
    gl.vertexAttribPointer(aPosition, 3, gl.FLOAT, false, 0, 0);

    // 激活attribute变量
    gl.enableVertexAttribArray(aPosition);

    const colorData = new Float32Array([
      1,0,0,1,0,0,1,0,0,1,0,0,1,0,0,1,0,0,        // 红色
      0,1,0,0,1,0,0,1,0,0,1,0,0,1,0,0,1,0,        // 绿色
      0,0,1,0,0,1,0,0,1,0,0,1,0,0,1,0,0,1,        // 蓝色
      1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,        // 白色
      0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,        // 黑色
      0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,        // 浅蓝色
    ])
    const colorBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, colorBuffer);
    gl.bufferData(gl.ARRAY_BUFFER, colorData, gl.STATIC_DRAW);
    gl.vertexAttribPointer(aColor, 3, gl.FLOAT, false, 0, 0);
    gl.enableVertexAttribArray(aColor);

    let eyex = 3;
    let eyey = 3;
    let eyez = 5;
    let deg = 0;

    function draw() {
      deg += 0.01;
      const rotate = getRotateMatrix(deg);
      const vm = getViewMatrix(eyex,eyey,eyez,0.0,0.0,0.0,0.0,0.6,0.0);
      const perspective = getPerspective(30, ctx.width / ctx.height, 100, 1);
      gl.enable(gl.DEPTH_TEST);
      gl.uniformMatrix4fv(mat, false, mixMatrix(mixMatrix(perspective, vm), rotate));
      gl.drawArrays(gl.TRIANGLES, 0, points.length / 3);
      requestAnimationFrame(draw)
    }
    draw();
  </script>
</body>
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